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High-dimensional entanglement and topological protection in nonlinear waveguide arrays

Alessandro Zecchetto, Arnault Raymond, Jean‐René Coudevylle, Martina Morassi, Aristide Lemaître, Fabrice Raineri, Maria I. Amanti, S. Ducci, F. Baboux

Published Sep 22, 2025• 0 citations
Publisher

Abstract

We demonstrate a nonlinear AlGaAs photonic chip generating biphotons with high-dimensional spatial correlations. Photon pairs are generated by parametric down conversion in a waveguide array and simultaneously spread through quantum walks along the various waveguides, allowing to generate various types of high-dimensional entangled states of light. We further implement the Su-Schriefer-Heeger model and demonstrate the topological protection of the SPDC process against disorder. These results highlight nonlinear waveguide arrays as a promising platform for exploring the interplay between nonlinearity, disorder and topology in quantum photonic circuits.

DOI
10.1051/epjconf/202533506005/pdf

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We demonstrate a nonlinear AlGaAs photonic chip generating biphotons with high-dimensional spatial correlations. Photon pairs are generated by parametric down conversion in a waveguide array and simultaneously spread through quantum walks along the various waveguides, allowing to generate various types of high-dimensional entangled states of light. We further implement the Su-Schriefer-Heeger model and demonstrate the topological protection of the SPDC process against disorder. These results highlight nonlinear waveguide arrays as a promising platform for exploring the interplay between nonlinearity, disorder and topology in quantum photonic circuits.
We demonstrate a nonlinear AlGaAs photonic chip generating biphotons with high-dimensional spatial correlations. Photon pairs are generated by parametric down conversion in a waveguide array and simultaneously spread through quantum walks along the various waveguides, allowing to generate various types of high-dimensional entangled states of light. We further implement the Su-Schriefer-Heeger model and demonstrate the topological protection of the SPDC process against disorder. These results highlight nonlinear waveguide arrays as a promising platform for exploring the interplay between nonlinearity, disorder and topology in quantum photonic circuits.
Harnessing topological effects offers a route to protect quantum states of light from imperfections, potentially enabling more robust platforms for quantum information processing. This capability is particularly relevant for active photonic circuits that generate quantum light directly on-chip. However, the impact of topology on the spectral properties of parametric processes, crucial for scalable quantum photonic circuits, remains largely unexplored. Here, we address this question by investigating photon-pair generation via spontaneous parametric down-conversion (SPDC) in nonlinear waveguide arrays, combining experiment and theory. A systematic comparison of uniform, trivial, and topological Su-Schrieffer-Heeger (SSH) arrays reveals that only the topological configuration preserves a stable SPDC resonance spectrum under coupling disorder, with fluctuations in the resonance wavelength reduced by more than an order of magnitude. An analytical model captures the origin of this robustness in the band-structure properties of the interacting modes. Numerical analysis further shows that each SSH array can operate as a robust photon-pair source, enabling stable interference between multiple such sources and the generation of high-dimensional entangled states with high fidelity. These results establish nonlinear waveguide arrays as a promising platform for harnessing the interplay of topology and nonlinearity in quantum photonic circuits.
The generation of multi-photon quantum states in integrated waveguiding structures provides a route to the creation of quantum optical chips. In particular, the simultaneous generation of photons through spontaneous parametric down-conversion (SPDC) and their quantum walks in nonlinear waveguide arrays (WGAs) can be used to produce strongly spatially entangled biphoton states [1] with applications for quantum search algorithms [2]. Whereas up to now only arrays of single-mode nonlinear waveguides have been considered for SPDC, in general the waveguides may support several guided modes, which were demonstrated to strongly affect nonlinear wave mixing in the classical regime [3]. Here we show that using higher order modes for SPDC has a significant influence on the generated two-photon states and gives additional means to control them. In particular, we employ the symmetry of the modes to engineer effectively nonlocal photon pair generation by SPDC.
Harnessing high-dimensional entangled states of light presents a frontier for advancing quantum information technologies, from fundamental tests of quantum mechanics to enhanced computation and communication protocols. In this context, the spatial degree of freedom stands out as particularly suited for on-chip integration. But while traditional demonstrations produce and manipulate path-entangled states sequentially with discrete optical elements, continuously coupled nonlinear waveguide systems offer a promising alternative where photons can be generated and interfere along the entire propagation length, unveiling novel capabilities within a reduced footprint. Here we exploit this concept to implement a compact and reconfigurable source of path-entangled photon pairs based on parametric down-conversion in semiconductor nonlinear waveguide arrays. We use a double-pump configuration to engineer the output quantum state and implement various types of spatial correlations, exploiting a quantum interference effect between the biphoton state generated in each pumped waveguide. This demonstration, at room temperature and telecom wavelength, illustrates the potential of continuously coupled systems as a promising alternative to discrete multicomponent quantum circuits for leveraging the high-dimensional spatial degree of freedom of photons.
Harnessing high-dimensional entangled states of light presents a frontier for advancing quantum information technologies, from fundamental tests of quantum mechanics to enhanced computation and communication protocols. In this context, the spatial degree of freedom stands out as particularly suited for on-chip integration. But while traditional demonstrations produce and manipulate path-entangled states sequentially with discrete optical elements, continuously-coupled nonlinear waveguide systems offer a promising alternative where photons can be generated and interfere along the entire propagation length, unveiling novel capabilities within a reduced footprint. Here we exploit this concept to implement a compact and reconfigurable source of path-entangled photon pairs based on parametric down-conversion in semiconductor AlGaAs nonlinear waveguides arrays.